56 PHYSIOLOGICAL CHEMISTRY. 



Ex. Note the solubility of small bits of tallow in ether, chloroform, 

 benzine and alcohol, using in each case the same volume of liquid, with 

 equal weights of fat. The solubility in alcohol will be found much less 

 than in the other menstrua. 



Ex. Dissolve some mutton or beef tallow in chloroform and with a 

 glass rod put two or three drops of the nearly saturated solution on the 

 center of a glass slide. As the chloroform evaporates a film begins to 

 form on the top of the drop. Now put on a perfectly clean cover glass 

 and allow to stand until crystallization is complete, which may require only 

 a few minutes or some hours, the time necessary depending on the tem- 

 perature and on the concentration of the solution. Examine the crystals 

 with a microscope. Use a power of 200 to 300 diameters. By repeating 

 the experiment with different fats considerable variation in the form of 

 the crystals may be noticed, which is shown in the annexed cuts. 



Ex. Add to 5 cc. of cottonseed oil half its volume of strong white of 

 egg solution and shake thoroughly. The liquids mix and form a white 

 mass or emulsion which, however, is not usually stable. 



Ex. To 5 cc. of cottonseed oil containing a little free fatty acid add 10 

 drops of strong sodium carbonate solution and shake. A good stable 

 emulsion is made in this way, as the sodium of the alkali solution forms 

 a soap with the free acid and this appears to form a film around the little 

 fat globules which prevents their flowing together again. 



Origin of Fats in the Body. The question of the forma- 

 tion of fats in the animal organism has been much discussed. 

 It was once assumed that like protein substances the fats are 

 products of the vegetable world only, and that the animal has 

 not the power of building them up from compounds which 

 are not fats. But this view is not correct as we have abun- 

 dant proof that fats may be made in other ways. Much has 

 been learned from the results of cattle feeding experiments 

 carried out in agricultural experiment stations, where the gain 

 in fat is often much in excess of what could be accounted for 

 by the amount of fats in the food consumed. This gain must 

 in some way be due to the effect of the carbohydrate and protein 

 substances in the rations fed. The fattening power of sugar 

 has long been recognized, but this has been in part accounted 

 for on the theory that the sugar acts to protect the fats of the 

 body from oxidation, by being readily oxidized itself to keep 

 up the body energy. But much evidence has been accumu- 

 lated to show that carbohydrates take part directly in the pro- 

 duction of fats. How this is accomplished is not known, but 



